Title page for ETD etd-1113103-113408


Type of Document Dissertation
Author Teng, Zheng
URN etd-1113103-113408
Title Rainfall-Runoff Control: Variably Saturated Transport for an Infiltration System Controlling Water Quality and Quantity
Degree Doctor of Philosophy (Ph.D.)
Department Civil & Environmental Engineering
Advisory Committee
Advisor Name Title
John J Sansalone Committee Chair
Donald Dean Adrian Committee Member
John H. Pardue Committee Member
Marty E Tittlebaum Committee Member
Charles W Lindau Dean's Representative
Keywords
  • filtration
  • rainfall-runoff
  • unsaturated flow
Date of Defense 2003-11-07
Availability unrestricted
Abstract
Rainfall-runoff impacted by anthropogenic activities transports significant quantities of particulate, aqueous and complexed constituents. These diffuse, unsteady and stochastic event-based loadings are unique challenges for water quality and quantity control. The design, water quality and quantity functions of a partial exfiltration reactor (PER) utilizing Fe-coated-sand and porous pavement (CPP) is examined specifically across three representative rainfall-runoff events. Total concentrations and mass for metals (Zn, Pb, Cu and Cd), suspended solids, and Chemical oxygen demand were reduced significantly. Rainfall-runoff volume and peak flow were reduced and time to peak was extended. Influent dm/dp ratios based on particle analyses suggest that the dominant PER particle separation mechanisms were physical-chemical filtration with the CPP layer functioning as a straining surface. The performance of the PER is a function of the unsteady site hydrology with a particle mass-based concentration removal efficiency ranging from 71 to 96 %. A 2D numerical model with Richardí»s equation was used to simulate the effluent hydrograph and water content profiles under transient hydraulic loadings illustrating the water quantity and water quality function of the PER. The exfiltration capacity of the surrounding soil met limitation with bypass occurring, when simulated for 1, 2, and 5 year design storm events. Evaporation dominants the drying process in the top layer of the PER, which can be dried out in 2 days in summer. The role of saturation degree, ionic strength, and media characteristics in variably saturated filtration was examined by bench-scale experiment. The breakthrough of suspended particles decreased with decreasing water saturation degree and with increasing ionic strength. Variably saturated flow filtration was proved to be more efficient than saturated flow filtration for concrete media. A dimensionless surface tension number NST was introduced to extend a trajectory saturated filtration model to variably saturated porous media. The relationship between unsaturated hydraulic conductivity and water content was developed by fitting gravimetric measurement data to the van Genuchten equation. Good agreement with experimental data supports the conceptual basis of the trajectory model with a combined gas-liquid interface adsorption term in addition to the straining, interception, and sedimentation mechanisms of the trajectory model for saturated flow.
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